Method of treating electric inlead conductors



March 30, 1954 E. E. KADUK 2,673,945

METHOD OF TREATING ELECTRIC INLEAD CONDUCTORS Filed Dec. 30, 1952Inventor": Edward E. KaduK,

His Attorney Patented Mar. 30, 1954 METHOD-OF TREATING ELECTRIC INLEAD ICONDUCTORS Edward E. Kaduk, Ma 'signor to General El ration of New Yorkyfield Heights, Ohio, as-

ectric Company, a corpo- Application December 30, 1952, Serial No.328,643

5 Claims. 1

The present invention relates generally to electric devices havingcurrent leading-in conductors having molybdenum portions extendingoutwardly from a sealed vitreous envelope and more particularly theinvention relates to methods for cleaning the exposed molybdenum partsof such conductors sealed directly into the wall of quartz envelopes ofelectric lamps.

In the manufacture of gaseous electric discharge lamps having quartzenvelopes and molybdenum leading-in wires having a flattened sectionsealed directly to the quartz envelope Without the interposition of asealing glass between the quartz and the molybdenum wire, the molybdenumwire is heated to about the softening temperature of quartz duringfabrication of the seal. Also, the step of exhausting the quartzenvelope after the seals between the leading-in wires and the quartzenvelope have been made and before the envelope is sealed off from theexhaust system is carried out at elevated temperatures.

During the above steps in the manufacture of such lamps a coating ofmolybdenum oxide forms on the inlead. Oxide formation is light duringfabrication of the seals between the inlead wire and the seal because ofinert gas, such as nitrogen, is used to surround the inlead during thisstep in the manufacture of the lamp. However, during exhaust of thequartz envelope with the inleads sealed therein oxidation is muchheavier at the parts of the molybdenum extending outwardly from the endsof the envelope because those parts of the inleads are at elevatedtemperatures and exposed to air during this step in the manufacture ofthe lamp.

An oxide coating on this portion of the inlead is highly undesirablebecause it creeps along the inlead and into the hermetic fused jointbetween the inlead and the quartz to make the seal gas pervious andterminate the useful life of the lamp.

The principal object of the present invention is to minimize duringmanufacture of the lamps the formation of molybdenum oxide on theexternal parts of molybdenum inleads of electric lamps having quartzenvelopes and to expeditiously remove the small amount of molybdenumoxide which does form on such parts. Further objects and advantages ofthe invention will appear from the following detailed description.

The invention attains its objects by first coating the external parts ofthe molybdenum inleads with magnesium oxide prior to the ex haustingstep in the manufacture of the lamp;

to minimize the formation of molybdenum oxide and after the lamp issealed off from the exhaust system the entire lamp is immersed in anon-alkali containing mixture of glacial acetic acid and hydrogenperoxide to remove from the exposed parts of the inleads the smallamount of molybdenum oxide formed in spite of the protective coating ofmagnesim oxide.

Heretofore the said external parts of the inleads have been coated withboron oxide prior to the high temperature exhaust of the envelope toreduce the formation of molybdenum oxides during exhaust. This waseffective for preventing the formation of excessive molybdenum oxide butit also formed a scale of oxides which was exceedingly difficult toremove.

The use of magnesium oxide in accordance with the present invention isequally as effective for protecting the inlead wires from excessiveoxidation and has the highly desirable characteristic of being readilyremovable by an acetic acid, hydrogen peroxide mixture as I havedemonstrated.

The best mode contemplated by me of carrying out the invention isdescribed below in con junction with the accompanying drawings in which:

Fig. l is a perspective view of a high pressure mercury vapor electricdischarge lamp showing the end portions of the inleads extendingoutwardly from each end of the tubular quartz envelope of the lamp.

Fig. 2 is a side elevational view of an apparatus useful for cleaningfrom a number of such lamps magnesium oxide coating from the said endportions of the inleads extending outwardly from the lamp envelope.

Referring to Fig. l of the drawing the lamp l illustrated has a tubularenvelope 2 consisting entirely of quartz and provided at each of itsends with pinch seals 3 and 4. A single molybdenum inlead 5 extendsthrough seal 4 and is connected to and supports the main dischargesupporting electrode 6. Two molybdenum inleads l and 8 extend throughthe other of said seals. The inlead 8 is connected to and supports themain electrode 9 and the inner end ill of the inlead 1 constitutes anauxiliary electrode for facilitating the starting of the main dischargebetween the electrodes 6 and 9.

The tubular portion of the envelope 2 of the completed lamp I is filledwith a discharge conducting starting gas, such as argon, at a fewmillimeters pressure and contains a measured amount of mercury,indicated at ll, sufficient to produce a high pressure, superheated,luminosity producing mercury vapor atmosphere dur-' ing operation of thelamp I. The electrodes 6 and 9 include a coil of fine tungsten wiresupporting a pencil of material of higher electron emissivity, such asthorium.

The inleads '5, I and 8 have flattened portions I2, I3 and I4,respectively, which are hermetically united with the quartz at the pinchseals 3 and 4. The end portions I5, I6 and I1 of the inleads 5, I and 8respectively extend outwardly from the pinch seals 3 and 4 forconnection with a suitable source of electric power.

Lamps having the above structure and enclosed in a sealed glass envelopehaving a base provided J with electrical contacts are commerciallyavailable in a 100 watt size and are known in the trade as EH-d lamps. V

In making the lamps the seals 3 and 4 are first made by heating thequartz at the ends of quartz tube to soften these ends and then pressingthe softened quartz tube portions together onto the flattened portionsI2, I3 and I4 of the inleads 5, I and 8 to form the flat, gas tight,pinch seals 3 and 4. During this operation the inleads 5, I and 8 aresurrounded by an inert atmosphere, such as nitrogen and only a slightformation of molybdenum oxide takes place.

In accordance with the present invention, after the pinch seals 3 and 4have been made and before the envelope 2 is connected to the vacuumsystem for exhaust through its quartz tubulation I9, shown as sealed offin Fig. l, a coating of magnesium oxide is applied to the exposed endsI5,

I6 and I! of each of the inleads 5, I and 8. This Y is accomplished bydipping the inlead ends 5, I and 8 into a suspension of about 100 gramsmagnesium oxide in about 500 cc. of a binder comprising preferably,nitrocellulose in butyl acetate.

A satisfactory binder solution is one containing 54 04-06% solids, asdynamite grade nitrocellulose, in a solvent of 60 parts butyl acetate toparts naphtha, by volume. Of course, any suitable method of applying thecoating, such as painting, may be used.

The envelope 2 with the ends of the inleads so coated is then heated inair to a temperature slightly below the softening temperature of quartzand exhausted of air through the tubulation I9 while being maintained atan temperature. The envelope 2 is then allowed to cool. The other usualsteps in the manufacture of such lamps, such as filling the envelopewith the starting gas and introducing the mercury, are then carried outand the exhaust tubulation I9 is sealed off as shown.

Of course, the binder is driven off during the high temperature exhaustto leave a protective coating of magnesium oxide on the inlead ends.

During the high temperature exhaust in air a heavier formation ofmolybdenum oxide takes place on the end portions I5, I5 and I! of theinleads in spite of the protective coating of magnesium oxide. Removalof this molybdenum oxide is necessary to avoid termination of the usefullife of the lamp I by the oxide creeping inward along the inleads 5, Iand 8 into the hermetic fused joints between the quartz and theflattened portions I2, I3 and I4 of the inleads and making these jointspervious to gas.

In accordance with the present invention the molybdenum oxide and alsothe magnesium oxide is removed from the end portions I5, I6 and I! ofthe inleads by immersing the entire lamp I in a elevated mixture ofglacial acetic acid (CH3COOH) and 30% hydrogen peroxide (H202).

The apparatus shown in Fig. 2 is suitable for treating a number ofbatches of the lamps I by immersing the lamps in the cleaning mixtureand comprises a Pyrex beaker of about 800 cc. capacity supported by 'aring stand 2I and an electric heater 22 having current leads 23 alsosupported by the ring stand 2| underneath the beaker 20.

In cleaning a number of the lamps I a mixture of 250 cc. ofglacialacetic acid and 150 cc. of 30% hydrogen peroxide is preheated in thebeaker 20 by the heater 22 to a temperature of approximately to C.,inclusive. A batch of lamps I, preferably about 50, is then placed inthe beaker. The mixture completely covers the lamps I.

Due to the cooling effect of the lamps the temperature'of the mixturemay drop below 80 C. in which event the heater is suitably energized toheat the'mixture and raise and maintain its temperature to within therange of approximately 80 to 90 C., inclusive.

With the first batch, the reaction proceeds slowly until a yellow color,due to the formation of peroxy-hexamolybdic acid, appears in themixture. After this color becomes apparent the oxides are removed fromthe exposed inlead ends I5, I6 and II of the lamps I of the first batchin about 5 to 7 minutes.

Of course, with subsequent batches of lamps cleaned by immersion in thesame mixture the reaction proceeds at the rate established after theyellow coloration appears in the solution when treating the first batch.Thus, the total immersion time for subsequent batches of lamps isapproximately 5 to '7 minutes. The original mixture may be used to clean'four batches of lamps, each batch containing 50 lamps.

The oxide coating is not completely removed from all the inlead ends I5,I6 and I! of the lamps I at exactly the same time so that visualobservation as well as elapsed time of immersion should be used todetermine'the time each batch is retained in the mixture.

The temperature range of 80 to 90 C. is preferred for the mixturebecause-at lowertemperatures the cleaning of the inlead'ends I5, I6 and[1 takes place at an appreciably slower rate and at temperatures higherthan 90 C. the action is too rapid and results in too much of an attackon the metal'of the inlead ends.

After the oxide coating has been removed from the inleads of one batchof lamps, the mixture is poured into another suitable vessel such as a800 cc. Pyrex beaker and the-clean lamps in the beaker 25] are washedwith cold tap water. Hot water should be avoided because its useoccasionally causes a brown film to appear on the inlea'd ends I5, I6and II. The step of rinsing the lamps with cold water should be doneprompt- 1y on the removal of the mixture to avoid discoloration of theinlead ends. Such a discoloration can be prevented also by placing -asmall amount of ammonium hydroxide in the beaker while running the tapWater thereinto.

After the lamps are washed thoroughly in the manner described above theyare air dried or oven dried at a. low temperature and are then ready formounting inthe usual glass envelope provided for such lamps in thecommercial lamps of the EH-4 type.

The same mixture may be poured back into the beaker 20 orretained in-thesame beaker in which-itwas placed when -rmsing-the lamps in the beaker20 and used for cleaning subsequent batches of lamps as mentioned above.

The use of the glacial acetic acid, hydrogen peroxide solution in themethod described above has a high degree of safety and is thereforeeminently satisfactory for use in factory production of the lamps I. Thereaction between the mixture and the molybdenum and magnesium oxideproceeds in an orderly manner when the lamps are immersed and does notincrease in violence or temperature while the chemical action is takingplace. On the contrary, the mixture must be heated for short intervalsduring the cleaning period in order to maintain a temperature within therange of so to 90 C. inclusive. A 30% hydrogen perioxide is preferredhowever for safety purposes initially. As the reaction proceeds wateralso is formed from the peroxide during the cleaning process thusproviding an added safety factor. During the heat ing cycle the openingin the vessel containing the mixture may be covered to prevent excessiveevaporation of water.

Another safety factor characteristic of the mixture is that it does notreact violently with mer cury. This is an important feature in view ofthe droplet of mercury l I contained in each of the immersed lamps I oneor more of which may be accidentally broken during the cleaning process.

The stability of the glacial acetic acid, hydrogen peroxide mixture isdue to the presence of an acid with the peroxide solution. The mixtureof about 1.66 parts glacial acetic acid and 1.0 part 30% hydrogenperoxide by volume utilized as a cleaning solution in the present methodboils at approximately 107 C. without copious evolution of oxygen and istherefore a safe solution for use as contemplated by the presentinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In the manufacture of electric lamps having quartz envelopes providedwith electrical conductors extending through and sealed directly to thewall of the envelope, wherein the portions of conductors exposed outsideof said envelope consist of molybdenum and wherein during exhaust theenvelope with the conductors so sealed therein is heated in air to atemperature such that formation of molybdenum oxide occurs on themolybdenum portions of the conductors exposed outside the envelope, themethod of protecting the said exposed portions of the conductors fromexcessive oxidation during exhaust of the envelope and of removing themolybdenum oxide formed on said conductor portions during the exhaust,which method comprises first applying a coating of magnesium oxide tothe said conductor portions prior to heating and evacuating saidenvelope and therea ter, when the manufacture of said lamp has beenotherwise completed, removing the molybdenum oxide and the magnesiumoxide from said exposed conductor portions by immersing at least thesaid exposed conductor portions of the lamp in a mixture of glacialacetic acid and hydrogen peroxide.

2. The method of treating electric inlead conductors sealed directlyinto the wall of a quartz envelope of an electric lamp and havingportions consisting of molybdenum exposed outside said envelope whichcomprises the steps of coating the said exposed molybdenum portions ofsaid conductor prior to exhausting said envelope at elevatedtemperatures with magnesium oxide to minimize the formation ofmolybdenum oxide on said conductor portions during the said exhaust ofthe envelope and, after completion of said exhaust and the other stepsin the manufacture of the lamp, removing the magnesium oxide and themolybdenum oxide from said exposed conductor portions by immersing theentire lamp in a mixture of glacial acetic acid and hydrogen peroxidehaving a temperature of about to 0., inclusive.

3. The method of treating electric inlead conductors as defined in claim2 characterized by the fact that a 30% hydrogen peroxide is used in themixture.

4. The method of treating electric inlead condoctors as defined in claim2 characterized by he fact that the mixture consists of 1.66 partsglacial acetic acid and 1.0 part 30% hydrogen peroxide.

5. The method of treating electric inlead conductors as defined in claim2 characterized by the fact that the mixture consists of 1.66 partsglacial acetic acid and 1.0 part 30% hydrogen peroxide and the fact thatthe lamp is retained in the mixture for a period of 5 to 7 minutes andis thereafter removed from the mixture and rinsed with cold water.

EDWARD E. KADUK.

No references cited.

1. IN THE MANUFACTURE OF ELECTRIC LAMPS HAVING QUARTZ ENVELOPES PROVIDEDWITH ELECTRICAL CONDUCTORS EXTENDING THROUGH AND SEALED DIRECTLY TO THEWALL OF THE ENVELOPE, WHEREIN DURING EXHAUST CONDUCTORS EXPOSED OUTSIDEOF SAID ENVELOPE CONSIST OF MOLYBDENUM AND WHEREIN DURING EXHAUST THEENVELOPE WITH THE CONDUCTORS SO SEALED THEREIN IS HEATED IN AIR TO ATEMPERATURE SUCH THAT FORMATION OF MOLYBDENUM OXIDE OCCURS ON THEMOLYBDENUM PORTIONS OF THE CONDUCTORS EXPOSED OUTSIDE THE ENVELOPE, THEMETHOD OF PROTECTING THE SAID EXPOSED PORTIONS OF THE CONDUCTORS FROMEXCESSIVE OXIDATION DURING EXHAUST OF THE ENVELOPE AND OF REMOVING THEMOLYBDENUM OXIDE FORMED ON SAID CONDUCTOR PORTIONS DURING THE EXHAUST,WHICH METHOD COMPRISES FIRST APPLYING A COATING OF MAGNESIUM OXIDE TOTHE SAID CONDUCTOR PORTIONS PRIOR TO HEATING AND EVACUATING SAIDENVELOPE AND THEREAFTER, WHEN THE MANUFACTURE OF SAID LAMP HAS BEENOTHERWISE COMPLETED, REMOVING THE MOLYBDENUM OXIDE AND THE MAGNESIUMOXIDE FROM SAID EXPOSED CONDUCTOR PORTIONS BY IMMERSING AT LEAST THESAID EXPOSED CONDUCTOR PORTIONS OF THE LAMP IN A MIXTURE OF GLACIALACETIC ACID AND HYDROGEN PEROXIDE.